[PATCH 12/15] x86: Remove !CONFIG_X86_TSC code

Ingo Molnar
2025-12-14T08:48:07Z

Now that the Kconfig space always enables CONFIG_X86_TSC (on x86),
remove !CONFIG_X86_TSC code.

We still keep the Kconfig option to catch any eventual code still
pending in maintainer or non-mainline trees, and it's also still
possible to disable TSC support runtime.

Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Ahmed S . Darwish <darwi@linutronix.de>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: H . Peter Anvin <hpa@zytor.com>
Cc: John Ogness <john.ogness@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20250425084216.3913608-13-mingo@kernel.org
---
arch/x86/include/asm/timex.h | 3 +--
arch/x86/include/asm/trace_clock.h | 8 --------
arch/x86/include/asm/tsc.h | 13 +------------
arch/x86/kernel/Makefile | 4 ++--
arch/x86/kernel/i8253.c | 2 +-
arch/x86/kernel/tsc.c | 13 -------------
6 files changed, 5 insertions(+), 38 deletions(-)

diff --git a/arch/x86/include/asm/timex.h b/arch/x86/include/asm/timex.h
index 956e4145311b..6e57e3c0fdd2 100644
--- a/arch/x86/include/asm/timex.h
+++ b/arch/x86/include/asm/timex.h
@@ -7,8 +7,7 @@

static inline unsigned long random_get_entropy(void)
{
- if (!IS_ENABLED(CONFIG_X86_TSC) &&
- !cpu_feature_enabled(X86_FEATURE_TSC))
+ if (!cpu_feature_enabled(X86_FEATURE_TSC))
return random_get_entropy_fallback();
return rdtsc();
}
diff --git a/arch/x86/include/asm/trace_clock.h b/arch/x86/include/asm/trace_clock.h
index 7061a5650969..1efab284c32a 100644
--- a/arch/x86/include/asm/trace_clock.h
+++ b/arch/x86/include/asm/trace_clock.h
@@ -5,17 +5,9 @@
#include <linux/compiler.h>
#include <linux/types.h>

-#ifdef CONFIG_X86_TSC
-
extern u64 notrace trace_clock_x86_tsc(void);

# define ARCH_TRACE_CLOCKS \
{ trace_clock_x86_tsc, "x86-tsc", .in_ns = 0 },

-#else /* !CONFIG_X86_TSC */
-
-#define ARCH_TRACE_CLOCKS
-
-#endif
-
#endif /* _ASM_X86_TRACE_CLOCK_H */
diff --git a/arch/x86/include/asm/tsc.h b/arch/x86/include/asm/tsc.h
index 4f7f09f50552..4d2d2f21ff06 100644
--- a/arch/x86/include/asm/tsc.h
+++ b/arch/x86/include/asm/tsc.h
@@ -76,8 +76,7 @@ extern void disable_TSC(void);

static inline cycles_t get_cycles(void)
{
- if (!IS_ENABLED(CONFIG_X86_TSC) &&
- !cpu_feature_enabled(X86_FEATURE_TSC))
+ if (!cpu_feature_enabled(X86_FEATURE_TSC))
return 0;
return rdtsc();
}
@@ -94,25 +93,15 @@ extern unsigned long native_calibrate_tsc(void);
extern unsigned long long native_sched_clock_from_tsc(u64 tsc);

extern int tsc_clocksource_reliable;
-#ifdef CONFIG_X86_TSC
extern bool tsc_async_resets;
-#else
-# define tsc_async_resets false
-#endif

/*
* Boot-time check whether the TSCs are synchronized across
* all CPUs/cores:
*/
-#ifdef CONFIG_X86_TSC
extern bool tsc_store_and_check_tsc_adjust(bool bootcpu);
extern void tsc_verify_tsc_adjust(bool resume);
extern void check_tsc_sync_target(void);
-#else
-static inline bool tsc_store_and_check_tsc_adjust(bool bootcpu) { return false; }
-static inline void tsc_verify_tsc_adjust(bool resume) { }
-static inline void check_tsc_sync_target(void) { }
-#endif

extern int notsc_setup(char *);
extern void tsc_save_sched_clock_state(void);
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index bc184dd38d99..19ebb67df142 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -94,7 +94,7 @@ apm-y := apm_32.o
obj-$(CONFIG_APM) += apm.o
obj-$(CONFIG_SMP) += smp.o
obj-$(CONFIG_SMP) += smpboot.o
-obj-$(CONFIG_X86_TSC) += tsc_sync.o
+obj-y += tsc_sync.o
obj-$(CONFIG_SMP) += setup_percpu.o
obj-$(CONFIG_X86_MPPARSE) += mpparse.o
obj-y += apic/
@@ -103,7 +103,7 @@ obj-$(CONFIG_DYNAMIC_FTRACE) += ftrace.o
obj-$(CONFIG_FUNCTION_TRACER) += ftrace_$(BITS).o
obj-$(CONFIG_FUNCTION_GRAPH_TRACER) += ftrace.o
obj-$(CONFIG_FTRACE_SYSCALLS) += ftrace.o
-obj-$(CONFIG_X86_TSC) += trace_clock.o
+obj-y += trace_clock.o
obj-$(CONFIG_TRACING) += trace.o
obj-$(CONFIG_RETHOOK) += rethook.o
obj-$(CONFIG_VMCORE_INFO) += vmcore_info_$(BITS).o
diff --git a/arch/x86/kernel/i8253.c b/arch/x86/kernel/i8253.c
index cb9852ad6098..0b991035f127 100644
--- a/arch/x86/kernel/i8253.c
+++ b/arch/x86/kernel/i8253.c
@@ -31,7 +31,7 @@ struct clock_event_device *global_clock_event;
*/
static bool __init use_pit(void)
{
- if (!IS_ENABLED(CONFIG_X86_TSC) || !boot_cpu_has(X86_FEATURE_TSC))
+ if (!boot_cpu_has(X86_FEATURE_TSC))
return true;

/* This also returns true when APIC is disabled */
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 7d3e13e14eab..5ad2c803d5a1 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -297,24 +297,11 @@ int check_tsc_unstable(void)
}
EXPORT_SYMBOL_GPL(check_tsc_unstable);

-#ifdef CONFIG_X86_TSC
int __init notsc_setup(char *str)
{
mark_tsc_unstable("boot parameter notsc");
return 1;
}
-#else
-/*
- * disable flag for tsc. Takes effect by clearing the TSC cpu flag
- * in cpu/common.c
- */
-int __init notsc_setup(char *str)
-{
- setup_clear_cpu_cap(X86_FEATURE_TSC);
- return 1;
-}
-#endif
-
__setup("notsc", notsc_setup);

static int no_sched_irq_time;
--
2.51.0